1. Field of the Invention
The present invention concerns a device to measure a radiation dose, in particular an x-ray radiation dose, of the type that absorbs radiation and provides an output signal dependent on the absorption which represents a measure for the dose.
2. Description of the Prior Art
In radiation image acquisition systems, in particular in x-ray systems as they are primarily used in medical diagnostics, it is necessary to regulate as precisely as possible the dose of the radiation that hits the patient to be examined. Typically an automatic dose regulator (Automatic Exposure Control) is used for this purpose, with either the radiation dose striking the detector or the unabsorbed radiation dose still present behind the detector being measured. The voltage generator of the x-ray tube is then regulated using this measurement value. Generally the duration of the emitted x-ray pulse is varied.
Conventionally, an ionization chamber disposed in front of the x-ray detector or the film cassette is used for such an automatic dose regulation. This ionization chamber (that normally has a number of planar absorption regions) provides an output signal, dependent on the degree of the absorbed radiation dose, which controls the generator. A disadvantage of such an ionization chamber is its absorption in the beam path (which interferes in particular in mammography) as well as its thickness (of up to approximately 12 mm) and as well as its tendency towards microphony.
As described, ionization chambers arranged in front of the detector or the film cassette interfere with mammography exposures due to the chamber size and the chamber absorption, which is why in such cases the dose measurement device is arranged behind the detector or the film cassette, and why a silicon diode is used for this purpose that absorbs the remaining x-ray radiation that is, for example, transmitted by the film-foil system and transmits an electrical signal that is in turn used for regulation.